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Failing PSU's, what do they put out ?


Level42
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I wonder if guys who encountered bad PSU's (not only the famous ingot) ever measured what was exactly coming out of those PSU's ?

 

I found one thread mentioning 11VDC from a Ingot, but how about others ?

 

Did they put out DC only, or maybe even AC, or DC with a high ripple ?

 

Maybe some guys still have bad PSUs and could measure them ?

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My brother fried a 130XE with an ingot. It was a mystery to him why it didn't work until a few months ago I saw he had an ingot and tested it with a multimeter. It's output was 9V or higher. We immediately cut the cord and tossed the AC end and brick, keeping the DIN end for future connection to a new 5VDC source.

 

That explained his dead 130XE. He remembers a distinctive 'pop' sound when he turned it on. <cringe>

 

I didn't have an oscilloscope to see the characteristics of the ugly power.

 

I also bought a 600XL of ebay lately, and saw the seller was including an ingot. I got a break on shipping after asking seller to do the same and just include the DIN side cord.

Edited by Nezgar
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  • 2 weeks later...

My brown/off white XL power supply (like one in top left in picture below) just died. Puts out 5V until computer is turned on, then drops to 2.4V. At least that didn't seem to damage anything in the computer. There's lots of room inside that unit, so I plan to replace the guts with a modern 5V 2A transformer. Used an ingot briefly, but boy does it get hot. Probably a good contributor to it's failure, if not placed in a well ventilated location. The ingot will be amputated as soon as I have the other functional again.

post-16281-0-29855300-1390020538.jpg

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Man I'd love one of those XL styled PSU......dead or alive doesn't matter....even just an empty box would be sweet....

 

Hey, can you make a picture of the inside ? I don't think I ever saw what's in it..... Is the height the same as a 600/800XL ?

If so the transformer is pretty shallow...

 

Also, that one must be easy to fix...

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Hey, can you make a picture of the inside ? I don't think I ever saw what's in it..... Is the height the same as a 600/800XL ?

If so the transformer is pretty shallow...

 

Haven't popped it open yet, and haven't been in one before so I'll post some pics here when i do, hopefully in the next few days.

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Here's what's inside. Bottom side of PCB says "CHELCO 1983 600XL/800XL POWER SUPPLY" - Nice it matches the PCB maker of my 600XL :) But wow, this function can be done in a whole lot less space these days...

 

Nice simple AC transformer in there, output of AC10V according to etchings where it connects to the PCB. Looking at the rectifier area components near the big 10000uF 16V Electrolytic capacitor, and some googling I've come up with these, any suggestion which component to replace first that would be failing under load? I don't think there's an easy way to find a fault with just my voltmeter. running a ohm check across the 2 1N5408 compared the same, and the 2 1N5402 compared the same to each other too.

 

4x tiny brown capacitors - 10 nF Capacitor - 103Z (Guessing these are the culprit)

2x black rectifier diode 1N5408
2x black rectifier diode 1N5402
0.1J 100V 0.1uF 100nF Polyester Film Capacitor (The green one on the underside)

 

Inside pics:

post-53052-0-57660000-1508051130_thumb.jpg

post-53052-0-13372700-1508051145_thumb.jpg

post-53052-0-15861400-1508051153_thumb.jpg

 

Cheers,

Ryan

Edited by Nezgar
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Yes, usually. The ram chips seem to sacrifice themselves

for the good of the community which brings the voltage

back down since they usually fail in shorted mode when

subjected to 7 volts or so by a failed voltage regulator

inside the ingot.

 

Our very own Flashjazzcat has a brilliant technique of

using alcohol spray to detect the shorted ram chips.

Atari 130XE board repair: Boots to red screen

https://www.youtube.com/user/flashjazzcat/videos

 

What you talking about Nezgar? You did the testing with

ohmmeter. Now pull the rotten 7805 voltage regulator and

power up without it to insure 10 volts DC are made on the

board, check for magic smoke, and then install a good 7805.

They don't always fail shorted, this one appears to just

have gone senile and forgot what his job was all about.

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Here's what's inside. Bottom side of PCB says "CHELCO 1983 600XL/800XL POWER SUPPLY" - Nice it matches the PCB maker of my 600XL :) But wow, this function can be done in a whole lot less space these days...

 

Nice simple AC transformer in there, output of AC10V according to etchings where it connects to the PCB. Looking at the rectifier area components near the big 10000uF 16V Electrolytic capacitor, and some googling I've come up with these, any suggestion which component to replace first that would be failing under load? I don't think there's an easy way to find a fault with just my voltmeter. running a ohm check across the 2 1N5408 compared the same, and the 2 1N5402 compared the same to each other too.

 

4x tiny brown capacitors - 10 nF Capacitor - 103Z (Guessing these are the culprit)

2x black rectifier diode 1N5408

2x black rectifier diode 1N5402

0.1J 100V 0.1uF 100nF Polyester Film Capacitor (The green one on the underside)

 

Inside pics:

attachicon.gifIMG_20171013_145353a.jpg

attachicon.gifIMG_20171014_225729.jpg

attachicon.gifIMG_20171013_150710_edit_b.jpg

 

Cheers,

Ryan

 

You can check the diodes with your meter in continuity mode - if current flows in one way but not the other, they're working. :) As for the caps, there are some meters that can test capacitance, but the tiny ones are so small it's not easy to determine if they're bad or if you're just getting screwy readings because the test leads are moving around or because you're bumping into the limits of accuracy or precision of your meter. The big one easier to test but if that one fails, it should be pretty obviously swollen, split and/or leaking.

 

If your meter has an AC mode and you're comfortable working with it powered up, you can at least see if the AC part of the transformer is putting out the right current and voltage, then you should be able to see which parts are failed empirically by testing along the current path.

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I was probing various points with the meter, and can confirm the 10VAC is good from the transformer.

 

But I think... to test the diodes properly they will have to be removed from the board, as I think the same traces are connected via the small brown capacitors, so it seems current is flowing through both simultaneously..

 

Working up to probing from bottom side while it's powered up :) also when computer is powered on, which is when the 2.5VDC problem exhibits itself.

Edited by Nezgar
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Are we sure there is a 7805 on it as 1050 suggests ? Maybe he has seen this PSU before and knows.

 

It certainly can be.....judging by the parts this is about as basic as a linear PSU can get.

 

Transformer->diode bridge-> filter cap -> 7805 with obviously controls a power transistor so that more amps are available than the 7805 alone can deliver.

 

Very very basic....

 

I would look at the 7805, but first check the transistor on other big heat sink (see B, C E marking) for shorts (use continuity / diode setting on your DVM).

 

The European FriWo's that usually came with XL's here were certainly a lot better built and contain some much more advanced regulation circuitry.....which reminds me that I need to see if there are schematics for that baby (or re-engineer one)....

 

 

But I still want one of those XL styled PSU's.....if anyone has a bad one....or even an empty one.....

 

 

(P.S. there isn't a 230V lug on the input on the transformer I guess ?) Even so, the transformer could easily be replaced.....

Edited by Level42
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Wait a minute.......that schematic.......your pictures.....it looks like there isn't anything on that second heatsink installed at all, right ?

 

So....they seriously left out the transistor but DID mount the huge, expensive heat-sink for nothing ?!?!?! WEIRD !

 

Also....a standard 7805 can cope with 1A MAX.

 

If I were you, I would replace it with a 7805CV-DG, wether it's defective or not. The -DG version can handle upto 1,5A, which gives a much needed bit of extra "space".

 

I have measured the current of an 800XL with a Blue Max cartridge inserted (thus music/sound playing and demo gameplay running) at about 800/850 mA....if you're going to add some add-ons in a system the 1000mA max is nearing fast....and don't forget that powering up _any_ device creates a start-up current well above "normal running" current.....I'm pretty sure the 7805 get's a good blow from every power up this way....

 

Apart from al that.......I hope there are some US Atari 8 bit PSU's that have a bit better configuration....

Edited by Level42
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Reading that article about the US power supplies made me think:

 

The writer correctly points out that the Type IV power supply, which uses an LM723 and external transistor has a certain risk: If the external transistor fails by shorting, the full input voltage will be supplied to the computer, surely damaging stuff... (It's a shame we will probably never know the inner workings of the Ingot, but I bet this has a set-up like this).

 

However, my favorite and much advocated European power supply by FriWo seems to have similar set-up with an external DIP IC and an "external" transistor............mmmmmmm....maybe this one isn't so safe after all....

Whatever you can say about the very basic 7805 only design....the 7805's usually fail by putting out lower voltages.......I don't think I've ever encountered a 7805 shorting it's input to the output...which does make it a pretty safe set-up....

 

Sadly the picture I took and uploaded to my Euro power supply thread doesn't show the IC markings because of flash reflection....now I want to open one and check....

 

221488-euro-power-supplies

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Thanks for the voltage regulator tip - I just phoned my local electronics shop, and the guy there has had experience with enough power supplies in general that he's also pretty confident it's the voltage regulator like you surmised, especially as you indicated the original 1A was probably not quite adequate. 1.5A seems to be the current minimum anyway. He highly doubts the caps are an issue unless you can visually see bulging, which mine seems pretty immaculate otherwise. Will stop in there tomorrow!

 

Now to unscrew the old voltage regulator from the heatsink, it looks like it was glued on, and just wont budge. Might have to dremel it out. :-D

Edited by Nezgar
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No, that's not glue you see, but silicone paste....this is needed to fill up the microscopic gaps between the metal of the 7805 and the metal of the heatsink so that the heat transfers from the 7895 into the theatsink without much resistance. You have to be careful as there might be also an insulating piece of mica (clear piece of sheet material, actually a kind of rock) which isolates electrically but transfers heat.

 

It looks like there is some locktite (red stuff) seal on the nut of the 7805. You'll need some force to unscrew that...you kind of "break the seal" when you do that....you'll understand what I mean when it happens ;). I always put some pliers or even better a correct socket over the nut and then unscrew the bolt/screw front the other side.

 

Ta a picture so we can see the 7805.....

 

By the way, I do assume you already checked the fuse right ? Measure it from the solder side, or ot least hold the measuring pins against the holder pens., although it doesn't look like it, I've had perfect fuses not making contact to the fuse holder from oxidation.....

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Heres the other side showing the L78S05CV. Tonight its working fine again... It's intermittent... But off the regulator i measure 10.6v without load, 9.8v with computer on. With computer on or off, i read 4.9v either way...

 

I wonder if i could solder in a second regulator as well on the other side? Would that split the load across the pair?

 

Regardless ill be getting some new ones tomorrow. Side note, Interesting I just checked a 1050, it uses a 7805 and 7812. Maybe new ones over there would fix some intermittent issues ive seen on some of those drives too. And maybe run cooler.

 

post-53052-0-59396500-1508211190_thumb.jpeg

 

Edit: Oh, and yes also measured same 10.8v across the big capacitor.

 

Cheers, Ryan.

Edited by Nezgar
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Mmmmm, whenever I hear intermittent I think: bad contact somewhere.

 

First check parts that move: the output cable to the computer would be suspect nr.1. There could be a break in it, usually near the DIN connector or near where the wire exits the supply.

Hook up the supply to a computer and power up....wiggle the cable near those spots and see what happens.

If that is solid, check the mains cable also near the plug and near the PSU itself are the most likely spots for breaks to happen, but since mains cables are much thicker it is far less likely to happen.

 

If that's not it, it could be a bad solder joint on the PCB.

 

By the way that 7805 is already a CV version.....and I bet 8840 means that it was produced in week 40, 1988.

The conclusion is that it must have been replaced already one time as I can't imagine this power supply to have been made in 1988.......or later...

 

It's also a messy job, leaving the excess silicone paste like that (I'm anal, I remove any excess with some alcohol and paper towel). They also screwed it in hard because it looks like the pins were soldered first and then they screwed it tight because all three pins are bent in the same angle....the correct way is first tightening the nut and bolt and only then solder the pins. This prevents mechanical stress on the solderings.

 

It's surprising they used locktite on the nut on the other side though...maybe it's just factory left-over.

 

Doesn't look like there's a mica and judging from the other pictures the heatsink doesn't look to be Hooked up to anything, maybe it's connected to ground but in that case you won't need a mica anyway....the metal backside of the 7805 is connected to the middle pin.....which is ground.

Edited by Level42
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